1. Field of the Invention
This invention relates to the art for determining the average molecular weight (Ma), average chain length (Dp) or dextrose equivalent (DE) value of starch and/or its related carbohydrates, including a polysaccharide or oligosaccharide containing glucose units, with convenience and high accuracy. The related carbohydrates may be hydrolysates from starch, including linear maltooligosaccharides like maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, maltoheptaose, or derivatives of starch or their hydrolysates, for example, ether derivatives, cationic derivatives, carboxyl derivatives. The invention is especially designed for use in the measurement of for example, sweetening agents corn syrup, food additives, and other industrial materials.
2. Description of Related Art
Starch and its related carbohydrates (hereinafter, the term "starch" will often be used to represent not only starch but also its related carbohydrates have been widely used a material or additive for manufacturing food, paper making, and other various industrial products. In such industrial applications of starch, it is important to the molecular weight (MW) of the starch to have an indication of its properties. For example, the molecular weight (MW) of a starch in a solution affects the viscosity of the starch solution, the hygroscopic property, in its sweetness in the case of corn syrup. Conventional methods for determining the molecular weight (MW) of a starch have been by measurement of intrinsic viscosity, light scattering, osmotic pressure, or speed liquid chromatography of the sample or by quantitative determination of the reducing terminals contained in starch. Of these methods the intrinsic viscosity method and the light scattering method include complicated processes to prepare the sample for measurement and the take a long time to complete a measurement. The osmotic pressure method is likely to be influenced the concentration of salt in the sample, and it is necessary to be careful in preparing the sample for this measurement method. Therefore these methods have been rarely employed except at the basic pre-industrial research stage. The high speed liquid chromatography is method versatile in determining average molecular weight (MW) as well as molecular weight distribution weight (MW) of a starch, but this method requires a standard sample for molecular weight (MW) determination, a complicated process for preparing sample to be measured and a relatively expensive apparatus, not to mention the method is time consuming. Accordingly, this method is also unsuited to industrial application.
Consequently, the most convenient method is the quantitative measurement of reducing terminals which includes a determination of total amounts of the reducing terminals and glucose units contained in a starch sample, and then a ratio of these two measurements if formed to represent the molecular weight (MW) of the starch. In the conventional art of determining the total glucose units, a determination of gross carbohydrate by the phenol and sulfuric acid method has been used, wherein strong acidic and alkaline chemicals are involved and heating is occasionally necessary. These factors pose problems in the disposition of waste chemical liquid and also are hazardous in operation. In view of such situations, for the sake of convenience, in the case where an outstanding starch solution does not contain any chemicals other than carbohydrates, the dried weight thereof was used as a substitute for the gross sugar amount. Thus, the DE value as the index of molecular weight is derived from forming a ratio between the dried weight as noted above and the quantitative amount of reducing terminals. However, actually starch is hygroscopic and this makes it difficult to know the correct dry weight.
Some of the methods for determining the amount of reducing terminals are to use organic agents which react to the reducing terminals and to use oxidation and reduction of ions such as Fe ions and Cu ions. Of these, above all, oxidation and reduction of Cu ion defines the best basis of measurement. That is, when divalent copper ions and a reducing sugar are heated in an alkaline solution, the copper is reduced to the monovalent state which may be quantitatively measured by colorimetry, spectophotemetry, or titration. However, this method has the disadvantage of heating a mass of an alkaline solution, a hazardous operation, and of producing a mass of waste liquid including copper. In addition, while the reducing sugar acts on the Cu ions by reduction, oxygen in the air tends to dissolve into the reacting solution, which causes re-oxidation of monovalent Cu ions. Thus, an error is produced. Requirements for preventing such an error includes a quick operation, sufficient skill, but actually the human error is significant.
Through the description above, it is clear that a means for determining the average molecular weight (MW), average chain length [hereinafter will be often referred to as molecular weight (MW) or equivalent] or DE value of a starch has a large industrial significance and that the need of a method and apparatus for determining this information with convenience and accuracy is presently needed.